1. Field of the Invention
The present invention relates to a method of controlling the proliferation of an aerobe, in which in the continuous culture of the aerobe by supplying a substrate and oxygen to a culture tank of the aerobe to cause the aerobe to decompose the substrate, the proliferation of the aerobe is inhibited while retaining the substrate-decomposing activity inherent in the aerobe.
2. Description of the Background Art
The culture of an aerobe, in particular, continuous culture has heretofore been used as an activated sludge process in a treating tank for purifying waste water such as, for example, organic sewage. In this activated sludge process, excess sludge is formed in a relatively great amount with the progress of the continuous culture of the aerobe, and most of such excess sludge is treated as industrial waste.
However, the industrial waste has been requested to decrease to a great extent from the viewpoint of environmental protection and in view of the trend of society. If only the proliferation of the aerobe can be inhibited without lowering the substrate-decomposing activity (purifying function) inherent in the aerobe, both reduction in treatment cost and decrease of industrial waste can be achieved. Such a method is hence extremely advantageous.
According to the activated sludge process, as illustrated in FIG. 1, waste water to be treated, which contains pollutant organic substances (substrate), is first adjusted to a pH, at which an aerobe is easy to act, in an adjustment tank 1 and then supplied to an aeration tank 2 in which the aerobe is being cultured. Air containing oxygen is supplied to the aeration tank 2 from a source of air supply 4, which is attached thereto, so as to aerate the aeration tank 2, whereby the pollutant organic substances (substrate) contained in the waste water is oxidatively decomposed by the action of the aerobe. In this case, a part of the organic substances is removed in the form of carbon dioxide by the substrate-decomposing action of the aerobe in the aeration tank 2, and at the same time, the aerobe proliferates to form an agglomerate (activated sludge). A part of the agglomerate is then discharged into a settling tank 3 together with the waste water purified.
In the settling tank 3, the agglomerate is precipitated and separated from the purified waste water, and the purified waste water is discharged as treated water from the settling tank 3. On the other hand, most of the agglomerate separated is discharged as excess sludge through a discharge duct 5 to treat it. The remainder of the agglomerate is returned as return sludge to the aeration tank 2 through a conduit 6 branched off from the discharge conduit 5.
In the activated sludge process, the amount of the excess sludge formed increases when the aerobe is continuously cultured in the aeration tank 2. Therefore, it is necessary to treat the excess sludge as industrial waste. As a method of treating the excess sludge, Japanese Patent Application Laid-Open No. 227191/1990 discloses a technique in which an alkaline substance is added to excess sludge, from which return sludge has been removed, to dissolve aerobes contained therein, thereby decreasing the excess sludge. However, the use of the alkaline substance as described above raises the pH of waste water after the activated sludge treatment. Therefore, an additional treating step is required for the pH adjustment and the like, resulting in unavoidable increase in cost. There is hence a demand for development of a technique capable of controlling the amount of excess sludge itself to be formed without subjecting the excess sludge to a special treatment.
In order to control the amount of the excess sludge to be formed, it has heretofore been conducted to regulate the amount of the return sludge returned to the aeration tank 2 or control the amount of oxygen-containing air to be supplied to the aeration tank 2 from the source of air supply 4 according to the concentration of pollutant organic substances contained in waste water to be fed to the aeration tank 2.
According to this method, however, the substrate-decomposing action of the aerobe in the aeration tank 2 is hindered though the amount of the excess sludge to be formed can be controlled. Such a method therefore involves a disadvantage that waste water treatment, which is the original object of the activated sludge process, is not sufficiently performed. In addition, the conventional methods cannot control the proliferation itself of the aerobe, and is hence not said to essentially control the amount of the excess sludge to be formed.